[issue 1164] Oom handling

[guicho271828]

Handle out-of-memory more gracefully.

• Alllocate a 1MB reserve memory in register_signal_handlers
• On OOM, release the reserve memory and throw ExitException with ExitCode::SEARCH_OUT_OF_MEMORY
• Unwind the stack to main, make sure to print the search statistics (reserve memory gives a leeway), return from main (which invokes destructors for shared_ptr objects)

https://issues.fast-downward.org/issue1164